1. Field of the Invention
This invention relates to a controllable hydro-elastic support mounted between two mechanical elements, subject to excitations and/or vibrations. More particularly, an elastic support when mounted between the engine and body of a motor vehicle is subjected to the vibration and excitation of the engine.
In the various stress conditions of the engine suspension, the following conditions are apparent:
The movements of great amplitude of vibration of the engine due to the sudden variations of engine torque are in the range between 0 and 10 Hz. To lessen these movements, the suspension must be stiff and damped.
The irregularities of the road induce vertical movements of the engine in the range between 10 Hz and 20 Hz. To reduce the harmful effects of these movements, the suspension must be damped.
When the engine is idling, it transmits vibrations to the body in the range between 15 Hz and 25 Hz. To insulate the body from these vibrations, the suspension must be flexible.
The masses in motion inside the engine generate forces of inertia which set the body vibrating, thus causing hummings in the range between 30 Hz and 300 Hz. To remedy this drawback, the suspension must be flexible.
The ideal response for the support is represented by the curves in solid lines shown in FIGS. 10A and 10B, FIG. 10A relates to the loss factor or phase shift, FIG. 10B relates to the stiffness of the support.
2. Description of the Related Art
Dampers are known that combine an elastic support of an elastomer and a hydraulic damping obtained by a throttling between two liquid chambers.
The variation in stiffness and damping as a function of frequency in these dampers is also known as shown by the dashed lines in FIG. 10B. At low frequency, the stiffness is close to the static stiffness, then goes to a continuous plateau of higher stiffness when the phase shift maximum is exceeded.
FIGS. 10A and 10B represent the variation in the damping (characterized by the loss factor tg .delta...delta.=loss angle), and stiffness as a function of the frequency.
The ideal response for the support is represented by the curves in solid lines shown in FIGS. 10A and 10B. The response of the standard support (which corresponds to a support according to the invention with a locked piston) is represented by the curves in dashes.
The curves in dashes show that the stiffness of a standard hydro-elastic support exhibits two plateaus as shown in FIG. 10B and that the loss angle has a bell-shaped variation as shown in FIG. 10A. Actually, in operation, the internal fluid goes from an upper cavity to a lower cavity by a duct; the effects of inertia cause the flow of the fluid in the duct to go through a maximum (corresponding to the maximum loss angle, point A in FIG. 10A), then to decrease to cancellation (minimum loss angle, maximum stiffness, point C to D in FIG. 10B).
It can be seen that this type of part provides a satisfactory behavior for a high damping (at 10 Hz to 20 Hz), but deviates from the ideal curve for the sudden variations in engine torque, idling and acoustics (at 0 to 10 Hz). Finally, the line comprised of small circles shows the response of the support with a free piston.